The AEM map sensor can read to about 32psi. You can use this device for not only lean condition trigger, but also an overboost trigger by simply setting the trigger points. If you plan on running more than 32psi, you can add a hobbs boost switch, and they come in many different options. The one I have selected to use is a 0-60psi switch. I have boost cut limit on the switch set to 38psi on my car, but you can set that anywhere desired, which is usually 2psi higher than your boost target.

For the lean condition trigger points. Typically on a BT car that moves a lot of air, the stock injectors will max around 22psi of boost pressure. So I have my trigger set to 22psi and all boost above that, then the afr trigger set at 12.8. When the failsafe sees 22psi and 12.8afr, it sends the ground signal to the 3port ebcs and opens the bov. As you can see by the charts, it is a soft cut, simply dumping some boost to keep the engine safe. This is not a hard fuel cut, so if you were near the end of the track chasing that 10 second pass, you won't smash your face off the dashboard. haha.

When running large amounts of aux fueling (anybody making more than 450hp in a speed3 or focus ST) you are heavily dependent on that aux fueling. When the stock PCM cuts fuel due to over rev, boost cut, FFS etc, the aux fueling is enough to continue to make the car run, hold peak boost, and when you see the datalog it is scary. The DI IDC is at zero, and the aux fueling is only enough to maintain a VERY lean condition while the engine is trying to make that powah. This usually ends in a catastrophic engine failure (melting things) This is why this wideband failsafe is a must have.

This can be configured to open the BOV, wastegate, cut spark if you are creative, or just about any trigger that you can supply ground to.

Here are a few diagrams, as you can see when I shut my meth off, and boost went over 22psi, it immediately dumped boost to a safe level.

Here is how I set up the AEM controller for my trigger points. This software is very easy to use. There is a USB cable coming off the back of the gauge assembly, you simply hook it to your computer, open AEM software that is a free download, and you can watch the gauge live, set up the display, the trigger points and even datalog right through the gauge.